Project Summary Tobacco use is high among adolescents of low socioeconomic status (SES). While tobacco regulation has contributed to steady declines in cigarette use among youth, these declines have occurred more quickly for high SES compared to low SES adolescents. Moreover, the proportion of polytobacco users (i.e., users of more than one tobacco product) has increased among adolescents. Polytobacco use among adolescents may be attributed to increasing popularity of alternative tobacco products (e.g., e-cigarette, blunts cigar, hookah, and smokeless tobacco). Polytobacco use among adolescents is concerning, as it may increase cancer risk and result in consumption of unknown or inconsistent concentrations of nicotine, which could interfere with brain development. Tobacco companies target consumers based on clearly defined user segments. Likewise, the success of tobacco regulatory efforts can be bolstered by a deeper understanding of how polytobacco use is segmented among adolescents. Our own studies of Connecticut youth have shown that low SES is associated with greater likelihood of polytobacco use. Although some research has started to examine trajectories of polytobacco use, to date, there are no studies that have examined latent classes of trajectories to show how youth progress across stages of use (i.e., never use to established user) for multiple products simultaneously. Additionally, a socioecological framework has yet to be applied to examine the mediators of the association between SES and polytobacco use. To address these gaps, this study aims to use longitudinal data (Waves 1-4) from the Population Assessment of Tobacco and Health (PATH) Study, a nationally representative survey, to: 1) examine group-based multi-trajectory models (and socioecologically-informed predictors) of youth use of cigarettes, e-cigarettes, cigar/cigarillo, hookah and smokeless tobacco and 2) conduct path analysis to examine environmental, social and intrapersonal mediators of the association between SES and polytobacco use. This study will produce evidence of: 1) distinct trajectories describing stages of polytobacco use and 2) how distinct elements of the environmental, social, and intrapersonal context, contribute to SES-based disparities in polytobacco use. Such evidence is especially important, as one cannot efficiently and effectively intervene to reduce polytobacco use without understanding how polytobacco use emerges and how it is sustained. Moreover, as noted in the National Cancer Institute?s (NCI) 2017 monograph on socioecological risk factors for tobacco use ?identifying mechanisms through which SES influences tobacco use may result in new potential targets for interventions that could ultimately reduce tobacco-related health disparities.?